On 12 Jun 2008 at 10:27, Bob Blick wrote:

> =

> On Thu, 12 Jun 2008 13:38:09 -0300, "Alexandre Guimar=E3es"
> <listas@logikos.com.br> said:
> =

> > 	Can you explain better how to do it with 2x sampling ? I have always
> > used 3 times and it works because it is able to detect the start bit in
> > at
> > least in the first third part of the start bit. How can you detect the
> > start
> > bit and take the samples consistently with 2x the baud rate ??
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> Hi Alexandre,
> =

> You caused me to look :) I used 4x sampling and got 9600 baud with 14MHz
> xtal. That is the method I show in the LCDterm:
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> http://bobblick.com/techref/projects/lcdterm/lcdterm.html
> =

> When I have done 2x sampling I could do 9600 baud with slower xtal but
> it is definitely less robust. The method was to set up a timer interrupt
> 19200 per second. Look for a start bit at the beginning of the interrupt
> routine, process incoming bits every 2 interrupts after that but process
> the incoming bits at the end of the timer interrupt, after the send
> routine and buffer routines. So there is less consistency in where the
> bit is captured but there is enough of a delay that if the start bit is
> detected at the very beginning you still get some margin.
> =

> Cheerful regards,
> =

> Bob
> =



	I have done soft-uarts using just 1x sampling.
	Detected the start-bit with an edge interrupt, set the next timer =

interrupt for 1.5 bit-time and the other interrupts for one bit-time.

	Never had a single problem but never used on noisy signals.

	Mark Jordan



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